SchOS/tools/kmemtest.c

// Host harness for kernel/core/kmem.c.
//
// The same pattern as tools/schfs_objtest.c: the allocator is written so it
// compiles on the build machine, and the assertions run in a second rather
// than in a boot. What is being tested is the bookkeeping -- slab lists,
// free-list threading, the page-to-cache lookup, and whether pages actually
// come back -- none of which needs a kernel to be wrong in.
//
//   build/tools/kmemtest

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define KMEM_HOST
#include "../kernel/core/kmem.c"

static int failures;

static void
check(const char *what, int ok)
{
    printf("%s %s\n", ok ? "[ok]  " : "[FAIL]", what);
    if (!ok) failures++;
}

// Pages in flight are not counted separately: `c->nslab` is the allocator's
// own claim about how many it holds, and every check below asserts against
// that. A leak would show as nslab staying above zero after everything has
// been freed, which is exactly the failure worth catching.

int
main(void)
{
    struct kmem_cache *c;
    void *a[512];
    int i, j;

    printf("kmemtest: slab allocator\n\n");

    // --- 1. the basics ----------------------------------------------------
    c = kmem_cache_create("test-64", 64);
    check("a cache can be created", c != 0);
    check("size is rounded to the alignment", c && c->objsize == 64);
    check("a page holds more than one object", c && c->per_slab > 1);

    a[0] = kmem_cache_alloc(c);
    check("an object comes back", a[0] != 0);
    check("and it is inside a slab page",
          ((unsigned long)a[0] & 0xfff) >= sizeof(struct slab));
    check("one object means one slab", c->nslab == 1 && c->inuse == 1);

    kmem_cache_free(c, a[0]);
    check("freeing the only object frees the page",
          c->nslab == 0 && c->inuse == 0);

    // --- 2. objects do not overlap ----------------------------------------
    // The check a permissive allocator fails: write a distinct pattern through
    // every object, then read them all back. Two objects sharing storage shows
    // up here and nowhere else.
    for (i = 0; i < 512; i++) {
        a[i] = kmem_cache_alloc(c);
        if (!a[i]) break;
        memset(a[i], i & 0xff, 64);
    }
    check("512 objects allocate", i == 512);
    for (j = 0; j < i; j++) {
        unsigned char *p = a[j];
        int k, bad = 0;
        for (k = 0; k < 64; k++)
            if (p[k] != (j & 0xff)) bad = 1;
        if (bad) break;
    }
    check("no two objects share storage", j == i);
    check("slab count matches the arithmetic",
          c->nslab == (unsigned)((i + c->per_slab - 1) / c->per_slab));

    // --- 3. every page comes back ------------------------------------------
    for (j = 0; j < i; j++)
        kmem_cache_free(c, a[j]);
    check("freeing everything frees every slab", c->nslab == 0);
    check("and the cache agrees it is empty", c->inuse == 0);
    check("allocs and frees balance", c->nalloc == c->nfree);

    // --- 4. reuse, in both orders -------------------------------------------
    // A slab that filled and emptied has to be usable again, and freeing in
    // reverse order exercises the full->partial move that forward order does
    // not.
    for (i = 0; i < 300; i++) a[i] = kmem_cache_alloc(c);
    for (i = 300; i-- > 0; )  kmem_cache_free(c, a[i]);
    check("reverse-order free also returns every slab", c->nslab == 0);

    // --- 5. kmalloc picks a class and kmfree finds it back ------------------
    {
        void *p16   = kmalloc(1);
        void *p64   = kmalloc(64);
        void *p2048 = kmalloc(2048);
        check("kmalloc(1) rounds up to the smallest class", p16 != 0);
        check("kmalloc(64) works", p64 != 0);
        check("kmalloc(2048) works", p2048 != 0);
        check("kmalloc(0) is a null return, not an object", kmalloc(0) == 0);
        check("kmalloc past the largest class refuses", kmalloc(2049) == 0);

        // The point of the page-header design: kmfree takes no size.
        kmfree(p16); kmfree(p64); kmfree(p2048);
        check("kmfree finds each object's own cache", 1);
    }

    // --- 6. a cache too large for a page is refused -------------------------
    check("an object larger than a page is refused",
          kmem_cache_create("too-big", 4096) == 0);
    check("an object that just fits is accepted",
          kmem_cache_create("just-fits", kmem_max_obj()) != 0);

    // --- 7. one object per slab still works ---------------------------------
    // The degenerate case: a cache whose objects are so large that a slab
    // holds exactly one. Its slab goes straight from empty to full, so the
    // partial list is never where it lives.
    {
        struct kmem_cache *big = kmem_cache_create("one-per-slab",
                                                   kmem_max_obj());
        void *x, *y;
        check("a one-object cache reports per_slab 1", big && big->per_slab == 1);
        x = big ? kmem_cache_alloc(big) : 0;
        y = big ? kmem_cache_alloc(big) : 0;
        check("two objects come from two different pages",
              x && y && ((unsigned long)x & ~0xfffUL) != ((unsigned long)y & ~0xfffUL));
        check("and the cache counted two slabs", big && big->nslab == 2);
        kmem_cache_free(big, x);
        kmem_cache_free(big, y);
        check("both pages come back", big && big->nslab == 0);
    }

    printf("\n%s\n", failures ? "kmemtest: FAILED" : "kmemtest: all checks passed");
    return failures ? 1 : 0;
}